Sterilization of starch



Patented June 11, 1946 I UNITED sTArEs PATENT orrica STERlhIZATION F semen August J. Bulfer, Berwyn, IlL, assignor to Corn Products Refining Company, New York, N. Y., a corporation of New Jersey No Drawing. Application December 13, 1943,

Serial No. 514,171

Claims. (0l. 127-71) This invention relates to the treatment of V step is eiiected' by washing the starch, Therestarch, more particularly corn (maize) starch, in after the starch is dried. Since the sterilization such manner as to render it free of thermophylic is-carried out in the wet state prior to drying bacteria. As used herein, the term thermophylic there is danger of recontamination of the starch bacteria refers to organisms of the aerobic and 5 during the drying step, as drying air very often anerobic types which resist, and propagate at, contains bacteria spores. Moreover, some of the high temperatures. 1 chlorine apparently becomes chemically attached An object of the invention is to produce a to the starch molecule so that not all of the starch which is substantially free of thermophylic chlorine is removed by the chemical agent. This bacteria, has good color and is free of foreign or residual chlorine is released from the starch ununpleasant taste and odor. Another object is der pressure cooking conditions as the starch is ,to provide a. method ofsterilizing starch to render used in the canning industry and produces an it free of thermophylic bacteria without appreundesirable thinning effect on the-starch. To ciably altering the viscosity characteristics of inhibit this thinning action of the chlorine upon the starch subjected to sterilization. A further the starch it is necessary to add to the starch object is to produce a starch free of thermophylic a certain amount ,of a neutralizing or buffering bacteria which gives a paste ofgood body, i. e., agent, e. g., di-sodium phosphate. The process one which retains its viscosity over a wide range is, therefore, somewhat involved and expensive. of cooking conditions. I have now found that I can produce a starch The invention will be found of particular adwhich is free of thermophylic bacteria, which revantage' in the preparation of starch which is tains its thick boiling character and which is in especially suitable for use by the canning trade. all other respects well adapted for use by the In the canning field, the starch used must fulfill canning trade, by a process which is simple and certain requirements. Thus, it must have an exinexpensive and which obviates various shorttremely low content of thermophylic bacteria, comings and disadvantages of processes hereshould have good color, should not have any fortofore known for the production of canning eign or unpleasant odor and finally, when cooked starch. In general, my invention embraces roast- 'should have a satisfactory body. The National -ing, i. e., dry heating, starch which is substan- Canners Association has established certain mina tially free of moisture, at a temperature of about imum standards concerning the content of ther- 240 to 260 F. for a period of about 1 to about 3 mophylic bacteria of both the aerobic and anhours. 4

erobic' types permissible in materials used in In carrying out the process of the invention canning foods. Starch treated according to the starch e. g., raw, unmodified corn starch, con-- present invention not only meets these standards taining 12% to 15% moisture, preferably in powbut also contains so far less than this permissible dered form, is rapidly dried as in a Huhn drier number of thermophylic bacteria ,that it may be or the like, to a relativelylow moisture content described as freeof thermophylic bacteria and' of the order of about 1% to 2% and, preferably will be referred to hereinafteras thermophylic not exceeding about 3%. In practising a prefree starch. In addition, it possesses the other ferred form of the invention, the dried-starch is properties above mentioned as desirable in a 40 thereafter promptly transferred to a roasting canning starch. device, such as a'dextrine cooker or the like. Various processes have heretofore been pro- This may advantageously be heated prior to the posed to produce starchv suitable for use by the introduction of, the starch, as to a temperature canning trade but none of these processes has approximating that at which the starch is to be proven wholly satisfactory. One of these methsterilized therein. The dried starch is then roastods, which is described in Kerr U. S. Patent ed at a temperature of about 240 to 260 F. for

2,332,320, involves treating the starch with chloa period of about 1 to 3 hours to effect the desired rine. While this process produces a satisfactory sterilization, The starch is then cooled, reeled product as concerns the provision of a low bacand packed in conventional manner.

terial content, it is not without some objection- In practising my invention one may use for exable features, It is necessary to remove the chloample, ordinary corn starch produced byany of rlne after the sterilizing action thereof and this the usual methods. Preferably starch to be is accomplished through the use of a chemical treated is in powdered form. In the conventional agent which, after it has served its purpose, must manufacture of corn starch the starch, after bealso be removed from the starch, This latter ingseparated from the germ, fibre and gluten of ture of the starch in the roasting the corn kernel, is washed and subjected to two or more filtering steps. as in an American filter,

and then dried to a moisture content of about 12% to 15% either in kilns or by flash drying. The resulting starch is known as pearlstarch and in general the invention contemplates the use of such starch, although other starches, and corn starch produced by other methods of manufacture or removed at difierent stages of the conventional process above described may be used.

The removal of moisture from the starch before it is subjected to the sterilizing treatment may be effected in any type of drier which is adapted to rapidly drive on the moisture from th'estarch and at the same time efifect removal of the released moisture vapor so as to minimize any opportunity for the starch to be modified to any appreciable degree. A commercial type of drier known as the Huhn drier is particularly suitable for reducing the moisture content of pearl starch or the like containing about 12% to 15% moisture, for purposes of the present invention. Such a drier may be used to efiect desired drying,'to

a moisture content of 3% or less, of starch containing up to 20% moisture, without modifying the starch appreciably. However, the moisture entering such drier should content of the starch not exceed 20%, in order to prevent any possible gelatinization of the starch in the drier. The drying of the starch by means of a drier of the Huhn type may be carried out in a single pass or in several passes in one driers.

Spraydrying processes or the like may also be used to remove moisture from the starch to be sterilized according to this invention. In the event a spray drying process is used, second American filter cake or the like may be suspended in water to a gravity of about 24 Baum and then this liquor spray driedto a moisture content of about 3% or less. v Alternatively, the spray drying of the liquor may also be carried out so that the moisture content of the starch is reduced to about 5% to 6% may be passed through a drier of the Huhn type or the like to further reduce the moisture content to about 3% or less.

The operation of the drying equipment should be so controlled that the temperature of the starch particles does not exceed about 130 to 140 F. at any time until after the moisture content of the starch has been reduced to about 3% or less, in order to prevent modification of the starch; although after the moisture content of the starch has been reduced to the desired level the temperature of the starch particles may be raised to a temperature as high as about 240 F. but not exceeding 260 F. In fact, it is convenient and advantageous to discharge the dried starch at a temperature of about 240 F. and to promptly transfer it to the roasting device so that the temperature at which it is delivered to the latter does not fall below about 230 F. Thus the sterilization of the dried starch may be commenced almost immediately upon introduction of the starch into the roasting device, whereas otherwise it would be necessary to raise the temperadevice to the sterilizing range hereinabove specified.

The temperature of the starch particles in the roasting device during sterilization should not exceed about 260 F., or be lower than about 240 F.; 250 F. is'the preferred sterilizing temperature.

The starch to be sterilized should not contain or in a series of such with a watch is the destruction of the bacteria and the lessthe modification of the starch. The aim in preparin the starch by drying for the sterilizing treatment should be to reduce the moisture content as low as may be feasible and expedient, and in any event below 3%. Under practical operating conditions, as when a drier of the Huhn type or the like is used to prepare starch for sterilization in accordance with the invention, the moisture content of the starch leaving the drier and entering the dextrine cooker or the like will vary between 1 and 2%.

Any type of rotating vessel having suitable provision for. indirect heating of the material charged thereto and equipped with agitating means sufficient to insure uniformity used to sterilize the starch. The conventional type of dextrine cooker or the like may be used satisfactorily.

Time is an impo tant factor in the sterilizing treatment and the starch should not be heated longer than necessary to effect the desired sterilization. In general, the period of time necessary for the sterilization of the starch will be from about 1 to about 3 hours, depending upon the moisture starch enters the roasting device, upon the temthe starch is maintained during the sterilizing treatment and upon the uniformity with which the starch is heated.

Raw corn starch, e. g., second American filter starch, treated according to the above described proces will have a Scott viscosity index of about 55 to 60, while the initial Scott index of the same starch, will be about -30 to 90, depending upon manufacturing condition the corn from which the starch is derived. The

Scott index which is referred to herein as a 4 measure of the hot paste viscosity of starch is determined as follows: J

Scott test-15 grams of commercial basis (i. e., including water) of 12% moisture starch is mixed with- 280 cc. of distilled water at room temperature.v The beaker containing the mixture is put into a boiling water bath and stirred constantly for five minutes by means of a mechanical agitator rotating at 200 revolutions per minute. At the end of five minutes the 'beaker is covered glass and the contents heated for another period of live minutes. At the end of ten minute the watch glass is removed, the condensate is drained back and the material stirred at the above rate, the draining and stirring taking ten seconds. The watch glass is put back on the beaker and the mixture heated for one minute and fifty seconds or until twelve minutes time has elapsed. The watch glass is' removed, the

' condensate is drained back into the beaker and content stirred, these operations taking fifteen seconds. At the end of twelve minutes and fifteen seconds, elapsed beaker is transferred to a Scott cup, described below, and at the end of fifteen minutes, total elapsed time, the plunger valve of the cup is withdrawn, allowing the paste to pass into a graduated cylinder arranged below the cup. The Scott index for any given paste is the number 'of 'hot paste vis- V of heating, may be content and temperature at which the and the character of time, the contents of the l Scott value with the Scott cup under test.

' secrets of second required for the delivery of 50 cc. of the starch paste from the cup. The Scott cup is a cup or funnel having a stainless stee1 cylindrical tube extending from the bottom. The in-- ternal diameter of the tube is 0.1168 inch and the length is 0.495 inch. This tube is screwed tion may be effected in the same apparatus by in effect transforming the drier device.

into a roasting to bring about desired sterilization of the starch.

I claim: V

1. The process of treating starch to render it substantially free of thermophylic bacteria. which comprises roasting starch having an initial moisexceeding about 3%, at a temperature of about 240 to 260 F. for a period oi about 1 to about 3 hours. i

2 producing thick-boiling thermophylic freestarch which comprises drying raw, unmodified starch to a moisture content not substantially greater than 3% at a temperature to effect such drying without substantially modi- 3. The process of producing thermophylic free corn starch having Scott viscosity ing the moisture content of rawfhnmodified-corn maximum of about 3% by drying the same at a starch temperature not exceeding' to F., and thereafter roasting the dried starch by drying the same at a ture not exceeding 130 to 140 F. until the moisture content of the starch has been reduced to a maximum of about 3%, continuing the drying of the starch at a starch temperature in excess of about 130 to 140 F., but not exceeding about 260 F., until the moisture content 01' the starch of about 240 period of about 1 to about 3 hours.

i AUGUST J. BULFER. 

